guardrail
noun
guard·rail
ˈgärd-ˌrāl
variants
or less commonly guard rail
plural guardrails also guard rails
1
: a railing that protects (as by preventing people from falling)
The sidewalk … is separated from the heavily treed ravine by a guardrail.—Jack Lakey
especially
: a barrier placed along the edge of a highway at dangerous points
The car swerved and hit a guardrail.
2
guardrails or less commonly guard rails plural
: protections against something undesirable : safeguards
Whatever the reasons for defaults, housing observers are most concerned that the guardrails put in place after the housing crisis are no longer there to help.—Andrea Riquier
often, specifically
: the methods, policies, and software used to prevent an artificial intelligence model from engaging in harmful actions (such as providing false information or exposing sensitive data)
Microsoft has built safety guardrails into Copilot that usually prevent the AI assistant from sending data to a bad actor. —Matt Binder
… called the model a national security risk after being notified of a jailbreak, or a way to get around its internal guardrails. —Hadras Gold
The general idea is to roll out AI tools with guardrails—that is, rules, policies and constraints. —Thad Rueter
Cite this Entry
“Guardrail.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/guardrail. Accessed 20 Oct. 2026.
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